Subcutaneous and intramuscular delivery of fluid medicaments by injection are common in the medical arts. Some medications, such as insulin, must be given frequently by injection to an individual. In many cases, these injections are self-administered. In other cases, injections are given to a large number of persons, such as inoculations to prevent disease. In any event, it is desirable that the injections be accomplished easily.
Many patients dislike needle injections due to pain, fear, and nervousness over needles. Additionally, practice has indicated there are serious risks related to needle injections. For example, blood-borne pathogens, such as HIV and hepatitis, can be transmitted to health care workers by accidental needle-sticks. Specific environments which have an exceptionally high risk of accidental needle-sticks include emergency rooms, county hospitals, and sites of mass immunizations. Also, the disposal of used needles is a growing concern. This disposal presents a problem to individuals other than healthcare workers. Children, for example, may find used needles in the trash, putting them at risk of contracting infection. Discarded needles likewise pose a risk to waste disposal workers.
Injectable medications are typically supplied in glass vials sealed with an inert rubber stopper. To administer the fluid medicament, the user must transfer the fluid medicament from the vial to a fluid medicament delivery device, such as a syringe and needle, or a needleless jet injector syringe. Transferring the fluid medicament adds cost to administering injections in a hospital or clinic because of the labor expense. Immunizing large populations requires administering many injections per hour, hence transferring the fluid medicament presents a significant time constraint. For the patient who must self-administer fluid medicaments, such as a diabetic patient requiring several insulin injections a day, transferring the fluid medicament can be an inconvenience. Also, with each transfer, there is an opportunity for error in the amount of fluid medicament being transferred and administered.
In an effort to eliminate transferring a fluid medicament from a vial, pre-filled glass cartridges have been developed. These pre-filled cartridges are similar in design to a syringe. One end is closed and includes either a needle or an inert rubber stopper. If a needle is not integral, then a needle subassembly that penetrates the rubber stopper is attached prior to use. A movable rubber plunger closes the end opposite the needle. To administer the fluid medicament, the pre-filled cartridge is placed in a device consisting of a holder and a driver that meets the movable rubber plunger. The user depresses the plunger to dispense the medication.
An example of the use of pre-filled cartridges is in the treatment of diabetes with multiple daily injections of insulin. A pre-filled cartridge contains an amount of insulin sufficient for several days. Insulin is then delivered from the pre-filled cartridge using a pen injector, a pen shaped device for injecting the insulin. A disadvantage of pre-filled cartridges, however, is that they still require using a needle to penetrate the skin and deliver the medication to the target tissue.
In efforts to minimize the fears and risks associated with needle injections, several types of needle-free jet injectors have been developed. These devices penetrate the skin using a high velocity fluid jet, and deliver medication into the tissue of a patient. In order to accomplish this, a force is exerted on the liquid medication. Jet injectors, in general, contain a fluid medicament which has been transferred into a chamber having a small orifice at one end. A ram is accelerated using either a coil spring or a compressed gas energy source. The ram impacts a plunger, which in turn creates a high pressure impulse within the chamber. This pressure impulse ejects the fluid medicament through the orifice at high velocity, piercing the skin. The energy source continues to apply a force to the plunger, which quickly propels the medication through the opening in the skin, emptying the syringe in a fraction of a second.
Neither glass vials containing multiple doses of a medication nor pre-filled cartridges can be used with existing jet injectors. This is because a significant amount of impulse energy is transmitted from the energy source. Although not directly impacted, the glass walls of the cartridge do not have sufficient strength to withstand the large amplitude pressure waves that result when the ram impacts the plunger. To withstand the stresses caused by the high pressures, existing jet injector syringes have thick walls molded from an impact resistant plastic, such as polycarbonate.
It is known that the amount of the fluid medicament delivered by any injection system must be accurate. To this end, manual syringes are available in varying sizes, marked for ease of reading and accuracy of medication dose. Control mechanisms for jet injectors vary depending on whether a single use, single dose is contemplated. When multiple doses are to be administered, controlling the amount of fluid medicament dispensed becomes more complex.
In light of the above, it is an object of the present invention to provide a medicament reservoir for use with a jet injector system. Another object of the invention is to provide a jet injector assembly to isolate the reservoir from the pressure waves created when the ram impacts the plunger. It is also an object of the present invention to provide a jet injector system which can use existing pre-filled cartridges. Yet another object of the present invention is to provide a high workload injector that draws a fluid medicament directly from a multi-dose vial.
Another object of the present invention is to provide an accurate and simple to use control mechanism to deliver predetermined amounts of a medication. Yet another object of the present invention is to provide a fluid medicament jet injector with a separate reservoir, which is relatively simple to manufacture, is relatively easy to use, and is comparatively cost effective.